My son, Gabe, turned two today and this was the train cake we made together. There were just a few of us celebrating and this cake was terrific because there were no leftovers. You could definitely customize it and add more cars depending on the size of your party.
This was also a big hit with Gabe because he is into trains at the moment and he got to help decorate it with all sorts of goodies. We originally got the idea from the Family Fun website. Check it out for lots of other cake ideas.